Dextran is a polysaccharide formed of glucose units, the chain lengthening of which is catalyzed by dextransucrase. Dextran is an α-D-1,6-glucose-linked glucan with variable side-chains 1-3 linked to the backbone units of the dextran polymer; this product should has different molecular weights (≥1000 Da), which influence characteristics of final solutions. The chemical and physical properties of native dextran powder change in function of the microbial strain from which it is produced and/or by the production method. The biosynthesis of dextran has been demonstrated in numerous bacteria, especially in Streptococcus mutans, Leuconostoc mesenteroides ssp. mesenteroides and Leuconostoc mesenteroides ssp. dextranicum. Leuconostoc produces the enzyme dextransucrase and secrete it into the culture medium in the presence of sucrose. This enzyme, dextransucrase, synthesizes dextran from the sucrose substrate, catalyzing the transfer of glucosyl residues from sucrose to dextran polymer and liberating fructose. The origin of the dextransucrase (i.e. the producing microorganism) influences the frequency and nature of the branch points of dextran molecule.
Dextran is an easily soluble, biocompatible and biodegradable polymer; commercial native dextran powder has applications in several fields. It is used especially in biochemistry as a support for filtration chromatography on a gel of the Sephadex type. Dextran could be used in cosmetic industry and in pharmaceutical compositions (see for example U.S. Pat. No. 5,902,800). Additionally, in the field of therapeutics, it is used as a substitute for blood plasma (Biochimie generale (General Biochemistry)—J. H. WEIL-Masson, 6th edition-1990-p. 171). Furthermore, dextran synthesized by a strain of Leuconostoc dextranicum is applied in the food industry for the texturing of food products such as yoghurts, cream desserts, milk-based drinks and salad dressings. European Patent Application Publication No. EP0363633 demonstrates the synthesis of dextran by a strain of Leuconostoc dextranicum and in particular by the strain Leuconostoc dextranicum NRRL-B-18242. Additionally, that patent application publication describes especially a composition containing dextran synthesized by this bacterium and the use of this composition in the food sector. The food application of dextran follows the trend of customers who want to prepare foods to be authentic, tasty and natural, turning away from those containing chemical additives. Natural additives—obtained trough fermentation—respond to food producers requests for natural options for ingredients, which result safe, reliable and sustainable. Dextran powder should be also utilized in bakery, as texturing agent, mainly in gluten-free sourdough, enhancing technical performances of the final products. At this proposal, high molecular weight dextrans (1-2·106 Da) have been approved by the European Union as a food ingredients in bakery products (Naessens M. et al., 2005).
Presently, searching for a bacterium, which is able to achieve high yields of heavy molecular weight dextran, is addressed to a species known as Weissella cibaria. W. cibaria is a species of Gram-positive, heterofermentative bacteria, placed within the family of Leuconostocaceae, which has been defined in 2002 (Björkroth K J, Schillinger U, Geisen R, et al., January 2002). “Taxonomic study of Weissella confusa and description of Weissella cibaria sp. nov., detected in food and clinical samples”. International Journal of Systematic and Evolutionary Microbiology 52 (Pt 1): 141-8). W. cibaria is a GRAS bacterium (Generally Recognized As Safe) by the United States Food and Drug Administration (FDA) and the genera is also included in the list of taxonomic units proposed by the European Food Safety Authority (EFSA, QPS list, Qualified Presumption of Safety). This strain should have a great importance because of many industrial applications. This species was isolated from a natural substrate and then it was selected after slime formation from sucrose. It has also been found to be hyper-productive in terms of dextran synthesis from sucrose.
The above strain of Weissella cibaria was accepted as a patent deposit under Accession Number 42196 at the NCIMB, Ltd International Depository, located at Ferguson Building, Craibstone Estate, Bucksburn Aberdeen, AB21 9YA, Scotland UK, on Nov. 28, 2013.